1. Field of the Invention
The present invention relates to a technique for improving a disk driving apparatus, and particularly to a technique for providing a disk driving apparatus having improved quality.
2. Description of the Related Art
In recent years, by providing a fluid dynamic bearing unit, disk driving apparatuses such as HDDs or the like have come to have dramatically improved rotation accuracy. Accompanying this dramatic improvement in the rotation accuracy, there is a demand for such a disk driving apparatus to have higher data density and higher data capacity. For example, with a HDD configured to magnetically store data, a recording disk on which recording tracks are formed is rotated at high speed. With such an arrangement, a magnetic head is configured to execute data reading/writing operations by tracing the recording tracks with a small floating gap between the magnetic head and the recording disk. In order to configure such a HDD with high data density and high data capacity, there is a need to narrow the width of each recording track. Furthermore, as the track width becomes narrower, there is a need to further narrow the gap between the magnetic head and the recording disk. For example, there is a demand to configure the magnetic head and the recording disk with a very small gap of 5 nm or less between them, giving consideration to data reading/writing reliability.
In many cases, such a disk driving apparatus includes a hub member configured to mount a recording disk. The hub member is supported by a base member via a fluid bearing unit. The fluid bearing unit includes a shaft and a shaft housing unit configured to house the shaft. A radial dynamic pressure groove is formed in at least one from among the outer face of the shaft and the inner face of the shaft housing member. By generating dynamic pressure in a lubricant fluid with which a space formed by the radial pressure groove is filled, the fluid bearing unit functions as a bearing. It should be noted that the hub member is connected to the outer face of the shaft (e.g., see Japanese Patent Application Laid Open No. 2003-289646).
With such a disk driving apparatus, in order to allow the hub member to be smoothly rotated relative to the base member via the fluid bearing unit, the hub member and the base member are arranged such that a gap is formed between them. With such an arrangement, the lubricant fluid with which the fluid bearing unit is filled gradually vaporizes into gas at a very low rate with the passage of the operating time of the disk driving apparatus. In some cases, such a gasified lubricant fluid passes through a gap between the internal components such as the fluid bearing unit, hub member, and base member, and leaks into a clean-air space housing a recording disk mounted on the hub member and a recording playback head configured to perform data read/write operations for such a recoding disk. The hub member is configured to be rotated at a high speed in a state in which the recording disk is mounted on it. Thus, the gasified lubricant fluid diffuses outward along the radial direction of the hub member due to airflow generated by the high-speed rotation operation. If the disk driving apparatus is used in this state for a long period of time, e.g., ranging from several months to several years, in some cases, a part of the gas component of the lubricant fluid adheres to the surface of the recording playback head to form a coating layer. If such a coating layer is formed on the surface of the recording playback head as described above, this increases the substantial distance between the recording playback head and the recording disk by the thickness of the coating layer thus formed. As a result, this increases the risk of the occurrence of data read/write error for the recording disk. That is to say, in some cases, this becomes a cause which shortens the life of the disk driving apparatus, i.e., a period of time during which the user can use this disk driving apparatus. Also, this becomes a cause of difficulty in enlarging the data capacity of such a disk driving apparatus.